X-ray tubes may be used in a variety of applications to scan objects and reconstruct one or more images of the object. For example, in computed tomography (CT) imaging systems an x-ray source emits a fan-shaped beam or a cone-shaped beam toward a subject or an object, such as a patient or a piece of luggage. The terms “subject” and “object” may be used to include anything that is capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of a detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis. The data processing system processes the electrical signals to facilitate generation of an image.
In general, in CT systems, the x-ray source and the detector array are rotated about a gantry within an imaging plane and around the subject. Furthermore, the x-ray source generally includes an x-ray tube, which emits the x-ray beam at a focal point. Also, the x-ray detector or detector array in some systems includes a collimator for collimating x-ray beams received at the detector, a scintillator disposed adjacent to the collimator for converting x-rays to light energy, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom. In other systems, a direct conversion material, such as a semiconductor (e.g., Cadmium Zinc Telluride (CdZnTe)) may be used.
The x-ray tube may include an emitter from which an electron beam is emitted toward a target. The emitter may be configured as a cathode and the target as an anode, with the target at a substantially higher positive voltage (which may be at ground) than the emitter (which may be at a negative voltage). Electrons from the emitter may be formed into a beam and directed or focused by electrodes and/or magnets. In response to the electron beam impinging the target, the target emits x-rays. The emitter may contain a number of electrodes used to set the local electric field on the emitting structure.
The voltage supplied to the electrodes of the emitter may be controlled to adjust the intensity or energy of x-rays that are generated. In these systems, with respect to controlling the emitter, it is desirable to be able to produce fast transitions from low to high voltages, as well as to produce slow changing waveforms between two or more electrodes voltage values. Conventional control systems and methods may add complexity and size to the overall system, and may not be able to cover the full spectrum of waveform profiles requested.